Lab 4- Christian Andrade

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City College University of New York Department of Electrical Engineering EE 32200 Saurabh Sachdeva Laboratory Report #4 Audio Amplifier (Part I) Christian Andrade Due date: 11/25/2022 Semester: Fall 2022

Audio Amplifier (Part 1) Introduction: The purpose of this lab is to design a common emitter audio amplifier using only standard (practical) resistors and components and then test its performance by determining the overall gain and the maximum input that can be amplified without distortion (clipping). Specifications and circuit schematics: The specifications for the common emitter audio amplifier are given in the following tables: As it can be seen we are asked to complete the values for the table 2 with only standard (practical) values for the resistors: We have arrived at the following values: R1: 1.2 K Ohms R2: 8.2 K Ohms RC: 1K Ohms RE1: 39 Ohms VBQ: 1.3 V VEQ: 0.83 V VCQ: 6 V

These values can be applied to the following schematic to implement the circuit: The purpose of CB is to filter out the DC component. After the capacitor undergoes the transients, it will act as an open circuit to DC and as a short to AC allowing the signal to enter unshifted by DC. The purpose of the CE is to stabilize the circuit and to prevent undesired oscillations. The following are the equations used to find the starting points for the simulation in order to get the typical gain of 20 asked as part of the specifications: RC=Zout = 1000Ω VCQ=6V IC = (VCC −VCQ) ⁄ RC = (12−6) ⁄1000 = 6mA re =VT ⁄ IC =25mV ⁄ 6mA = 4.33Ω RE1 = (RC⁄Gain) − re = 1000⁄20 − 4.167 = 45.67 Ω (we used 39 Ohms) VE = (RE1 + RE2) IC = (45.67 + 100)6mA = 0.874 V VB =VE +VBE =0.875+0.7=1.574V

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VB = VCC [R1⁄ (R1 + R2)] Z1 = (R1*R2) / (R1+R2) R2 = (VCC ⁄ VB) Zin = (12 ⁄ 1.574)1000 = 7624 Ω (we used 8.2kΩ) R1 = R2Zin ⁄ (R2 − Zin) = (7624 × 1000) ⁄(7624 − 1000) = 1151 Ω (we used 1.2kΩ) DC Bias Point Analysis: In this section we have performed a simulation to obtain the DC bias point for the following voltages: 50mVpp, 500mVpp, 1Vpp, and also the maximum voltage possible (pp) without clipping. Brief discussion about distortion (clipping): Depending of the amplitude of the signal (peak to peak) used we can see some clipping on the amplified signal output. This occurs due to the fact that the input signal is too high and that produces a clipped output. 50mVpp input: 500mVpp input:

1Vpp input: 150mVpp:

We have found that the signal input of 500mVpp and 1Vpp have clipping. The signal of 50mVpp is not distorted but is very weak. Lastly, we have found empirically that the maximum input signal we can get without clipping is 150mVpp. Laboratory Results: The following is a screenshot of the oscilloscope image produced by the circuit with 10Hz oscillations frequency:

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We can see in this graph that the circuit meets the specifications given at the beginning because it amplifies the signal with its specific gain asked. Oscilloscope image with a 10KOhm resistor In this case we can also see that the result is as expected giving the desired gain for the input signal. Gain vs Frequency: We have performed a manual measurement of the gain at different frequencies in order to verify that the gain is relatively constant for certain frequencies. The tabulated result is as follows: Frequency (Hz) Vin (mV) Vout (mV) Gain (Vo/Vi) 10 230 1500 6.521739 20 230 3200 13.91304 40 230 5360 23.30435 70 230 7360 32 100 230 8080 35.13043 150 230 8640 37.56522 300 230 9100 39.56522 600 230 9200 40 1000 230 9300 40.43478 3000 230 9300 40.43478

We can see that the gain is approximately constant at frequencies higher than ~ 300 Hz. Given the fact that human hearing ranges from a frequency of 20Hz to 15kHz, we can see that the audio amplifier will work pretty well, especially when the frequencies are higher than 300Hz. Conclusion: In this experiment we were able to simulate and implement a common emitter amplifier that will meet the specifications given. This amplifier will give an approximately constant gain for all frequencies that range from 300Hz to 15kHz although it will not amplify very well those signals that are below that threshold as can be seen in the graph, following an exponential response. This data gives us the following plots: 1 10 100 1 10 100 1000 10000 GAIN FREQUENCY (HZ) GAIN VS FREQUENCY Gain